The student engineer of a campus
radio station wishes to verify
the effectiveness of the lightning
rod on the antenna mast
(Fig. P18.57). The unknown
resistance Rx is between points
C and E. Point E is a “true
ground” but is inaccessible for
direct measurement because the stratum in which it is located is several meters below
Earth’s surface. Two identical rods are driven into the ground
at A and B, introducing an unknown resistance Ry. The procedure
for finding the unknown resistance Rx is as follows. Measure
resistance R1 between points A and B. Then connect A
and B with a heavy
between points A and C. (a) Derive a formula for Rx in terms of
the observable resistances R1 and R2. (b) A satisfactory ground
resistance would be Rx < 2.0 Ω. Is the grounding of the station
adequate if measurements give R1 = 13 Ω and R2 = 6.0 Ω?
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